Third generation (3G) mobile radio standards (e.g., Code Division Multiple Access (CDMA) 2000, Universal Mobile Telecommunications Systems (UMTS)) for wireless communication systems have been undergoing development since the mid-1990s. 3G standards initially supported data rates up to 2 megabits per second (Mbps), but have since evolved to support data rates up to 14 Mbps. Asymmetric 3G wireless user services (e.g., web browsing) requiring high downlink capacity (e.g., from a wireless base station to a wireless mobile device) led to the development of the High Speed Downlink Packet Access (HSDPA) standard and the Evolution Data and Voice (EV-DV)/Evolution Data Optimized (EV-DO) standard.
In 3G standards, CDMA transmissions on a downlink path are typically designed to be orthogonal at a transmitter. However, multipaths can destroy the orthogonality thereby resulting in significant inter-code/inter-path interference at a wireless receiver. In the context of 3G, orthogonality refers to the use of spreading sequences that are orthogonal to each other, that is, there is no correlation between a first spreading sequence and a second spreading sequence. The lower the CDMA spreading factor being utilized, and the closer a user is located to a wireless base station, the more deleterious the effects of interference due to multipaths become. Unfortunately, high data-rate wireless systems such as EV-DV/EV-DO and HSDPA for UMTS employ a low spreading factor and may utilize a scheduling rule that tends to select users that are close to the wireless base station and, thus, compound multipath interference effects.